Distribution of western beaufort sea polychaetous annelids

Depth and depth-related processes appear to exert primary control over the distributional patterns of species of polychaetous annelids in the western Beaufort Sea (Cape Halkett to Barter Island, Alaska). Species richness and total polychaete abundance are maximal along the outer continental shelf and upper continental slope. Stations exhibiting the most similar polychaete assemblages are located at similar depths. However, some species distributions appear to correlate better with sediment type than with depth. Maximum abundance occurs deeper on the continental slope to the west, and station clusters generated by non-hierarchical clustering (using the dominant polychaete species data) are not sorted strictly by depth. In a canonical analysis of discriminance, the station clusters were projected onto a two-dimensional plane in species space. The first and second canonical variables of the station clusters correlate with sediment grain-size distributions, suggesting a relationship between polychaete distribution patterns and the sedimentary environment. This relationship is further substantiated when sediment grain-size distributions for each station are plotted on a tertiary diagram: the stations are grouped and ordered in a pattern similar to that generated by the canonical analysis of discriminance.     

Spatial variability of infaunal nematode and polychaete assemblages in two muddy subtidal habitats

Spatial variation of populations and their assemblages is an important component of many aspects of ecology, including the maintenance of species diversity. In nature, organisms are generally aggregated in patches or form gradients or other spatially related patterns. This investigation quantified the degree of spatial structure in benthic invertebrate assemblages. It examined the distribution of infaunal assemblages of different size, mobility and contrasting life-history strategies (i.e. meiofaunal nematodes and macrofaunal polychaetes) in two offshore muddy habitats in the Celtic Deep and the NW Irish Sea off the west coast of the United Kingdom. The more heterogeneous habitat in the NW Irish Sea was characterised by higher tidal stress and bottom temperature while greater water depth, mean particle diameter and organic carbon content was typical for the comparatively homogeneous environment in the Celtic Deep. In both habitats, the environmental conditions became increasingly dissimilar with separation. A total of 125 nematode and 88 polychaete species were recorded with 69% of the nematode and 49% of polychaete species present at both study sites. Occurrence frequency of species, species diversity and average similarity of assemblage composition was higher in the Celtic Deep than in the NW Irish Sea. Results from correlation analyses revealed statistically robust relationships of community similarity and sample distance. Given their small size and low mobility, nematodes were more susceptible to within-habitat physical variability than larger-sized, more mobile polychaetes. This, coupled with limits to long-distance dispersal and likely restrictions in gene flow, resulted in a significant decrease in community similarity with distance at the spatial scales sampled (i.e. within 0.1–23 km). Polychaetes, in contrast, combined a higher dispersal potential (>23 km) with a relatively high tolerance to within-habitat environmental variability and these were the most likely causes for non-significant relationships between the similarity of their assemblages and sample distance. The potential mechanisms causing the observed variation and implications of results for environmental management strategies are discussed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Relationship between depth, sediment, latitude, and the structure of benthic infaunal assemblages on the mainland shelf of southern California

A regional benthic survey was conducted in 1994, and the data were used to assess the relationship among three habitat factors (depth, sediment grain size, and latitude) and the distribution of benthic infaunal assemblages on the southern California coastal shelf. Benthic samples were collected with a 0.1 m² Van Veen grab from 251 sites on the continental shelf (10–200 m deep) from Point Conception, California, to the United States–Mexico international border. The relationship between habitat and assemblages was investigated by conducting a Q-mode cluster analysis to define groups of stations with similar species composition and then examining whether differences were present in physical habitat attributes among those groups of stations. Analysis of data from 175 uncontaminated sites yielded four habitat-related benthic infaunal assemblages along the southern California coastal shelf: a shallow-water assemblage from 10–32 m, a mid-depth assemblage between 32 and 115 m, and two deep-water (115–200 m) assemblages, one in fine and one in coarse sediments. These empirically defined points in the depth and sediment grain size gradients can be used to define reference habitats for the development of biocriteria. Benthic abundance and diversity were greatest in the mid-depth assemblage, conforming to predictions for benthic assemblages in regions of upwelling. Within the 500 km of coastline examined, latitude was not an important factor in defining assemblages. Received: 3 December 1999 / Accepted: 9 October 2000     

Species-specific effect of macrobenthic assemblages on meiobenthos and nematode community structure in shallow sandy sediments

Three functionally different macrofaunal species (the filter- and/or surface deposit-feeding polychaete Hediste diversicolor, and the suspension-feeding bivalves Mya arenaria and Cerastoderma glaucum) were introduced as single- and two-species treatments into microcosms containing sandy sediment with a natural meiofaunal community. H. diversicolor is a burrowing species building a system of galleries, C. glaucum lives actively near the sediment surface acting as a biodiffuser and M. arenaria buries deeply and leads a sessile lifestyle. It is shown that H. diversicolor extended the vertical distribution of meiofauna into deeper sediment layers compared to the control and non-Hediste treatments. The response of the nematode community varied significantly among treatments and was dependant on the macrobenthic species composition but not on the species number. Nematode assemblages in all treatments with the polychaete, both in monoculture and with either bivalve, differed significantly from those recorded in other treatments and were more similar than replicates within any other single treatment. H. diversicolor also appeared to have stimulated nematode species diversity. The present study demonstrated that the impact of macrobenthic assemblages on meiofauna is not a simple summation of individual species effects but is species specific.     

Benthic invertebrate assemblages of Delaware Bay

During two consecutive summers, the first quantitative bay-wide survey (207 stations) of benthic invertebrates was conducted in Delaware Bay (USA). In 1972, 109 species were collected at 105 stations; and in 1973, 125 species were collected at 102 stations. A total of 169 different species were collected for both summers. The number of species and number of individuals increased with increasing salinity and increasing median grain size. These relationships were compared and were found similar to those in estuaries and bays throughout the world. Average density was 722 individuals m², which is low compared to other estuaries. The relationship of low secondary production to pollution, macroscopic algae, sediment transport, predation, and hydrography is discussed. Deposit feeders comparised the major feeding type. Local species composition was similar to that in Chesapeake Bay, and dominant species occurred in estuaries throughout the Mid-Atlantic Bight. The benthic invertebrates of Delaware Bay were related to the cosmopolitan mode of estuarine faunas. Faunal assemblages were identified by cluster analysis. The assemblages were associated with sediment type and salinity. It was concluded that Delaware Bay comprises a mosaic of animal assemblages, some of which have relatively sharp boundaries similar to classical level bottom type communities, whereas the boundaries of others are almost impossible to detect, and these represent species distributed along an environmental continum.     

Research On Zooplankton in the Gulf of Rapallo

Zooplankton samples, collected in autumn 1996 from two stations in the Gulf of Rapallo, Ligurian Sea (Rapallo Harbour and Prelo Bay, which is a more open site with lower human impacts) were analysed. at both stations, the community was dominated by copepods (mainly juveniles and adults of different species of Acartia and Oithona) and meroplankton (mainly polychaete larvae). Total zooplankton abundance in the harbour waters was significantly higher than in the nearby bay. the occurrence of Acartia grani in Rapallo Harbour and Pteriacartia josephinae in Prelo Bay is noteworthy, as they are reported for the first time in the Ligurian Sea, and A. grani has not previously been recorded to the Italian coastline. A three-day benthic chamber experiment aimed to quantify nutrient fluxes between the sediment and water column was performed in the Rapallo Harbour: the profound effects of confinement on the composition and abundance of zooplankton within the incubation chamber are discussed.     

Sediment disturbance and loss of beta diversity on subtidal rocky reefs

How changes in environmental complexity and heterogeneity affect beta diversity is poorly known. We investigated patterns of beta diversity in subtidal assemblages of algae and invertebrates in the northwest Mediterranean in relation to inclination of the substratum and sedimentation. Vertical and horizontal substrata supported distinct assemblages under low, but not under heavy, ambient loads of sediment. To test the hypothesis that sediment reduced the dissimilarity between assemblages, sedimentation was increased experimentally in plots established on vertical and horizontal surfaces at sites experiencing low ambient levels of sedimentation. Patterns were compared to those occurring at unmanipulated sites and at sites exposed to heavy loads of sediment about 2 km apart. After one year, assemblages on vertical substrata were indistinguishable from those occurring on flat surfaces at manipulated sites and both converged toward those occurring at sites exposed to heavy loads of sediment. Control sites still supported distinct assemblages on vertical and horizontal substrata by the end of the experiment. Similar effects of sediment were observed on recovering assemblages in experimental clearings. These results show that sediment increased similarity in assemblages overriding the influence of habitat complexity on beta diversity at small and large spatial scales.     

Benthic polychaetes in the Ratnagiri bay, India: influence of anthropogenic factors

Study of changes in macrobenthic community structure is an intrinsic part of many environmental monitoring programmes. Hence, it is pivotal to distinguish the effects of natural and anthropogenic factors on these sensitive organisms for accurate assessment and management of coastal environment. Polychaete species diversity of five stations in the Ratnagiri bay was investigated during premonsoon and postmonsoon months in 2007. Though no spatial trends in polychaete diversity vis-à-vis the pollution was visible, the polychaete univariate indices were uniformily better in premonsoon indicating clear seasonal trends. Shannon diversity values ranged from 1.4-2.4 during premonsoon and 0.6-1.6 during postmonsoon. Station 5, which was most impacted by anthropogenic wastes as demonstrated by the anoxic conditions coupled with higher nutrient load, had comparatively higher H' values (1.9 and 1.6) and better evenness values (0.9 and 0.7) during both seasons indicating that the polychaetes were not influenced by anthropogenic contamination. The study indicates that the polychaete distribution and diversity in the bay were governed primarily by variations in sediment texture rather than the anthropogenic disturbances.     

Some factors affecting the colonization of a dredged channel

Standing crop, population size, and species diversity of the macrobenthic organisms in an estuarine channel were studied before and after dredging. A new suction-corer which sampled an area 0.1 m² to a depth of 30 cm was used in order to insure the inclusion of large, deep-dwelling animals. Eleven months after dredging, biomass and number of species and specimens had not recovered to pre-dredging levels. Colonization began with relatively large, swiftly moving forms such as the errant polychaete Nereis succinea and the crab Neopanope texana sayi. Stations in silt and mud regions recovered more slowly than those in sandier sediments. Most of the dominant and subdominant species had not recovered 11 months after dredging, and the previously abundant polychaetes Notomastus latericeus and Clymenella torquata had virtually disappeared. Only relatively uncommon lamellibranchs such as Tellina agilis, Lyonsia hyalina and Mulinia lateralis increased after dredging. Distribution of sediment types changed as the result of modified tidal velocities in the channel. Mud and silt were removed by the dredge, exposing the sand underneath, and sandy stations became muddier as the result of lowered current velocities. Marked changes in species composition reflected this change in sediment character. Eleven months after dredging no evidence of succession was found, but colonization had begun. Values of all three parameters studied were reduced to small fractions of pre-dredging levels, although species diversity in sandy sediments exceeded pre-dredging levels.     

Polychaete assemblages along a rocky shore on the South Adriatic coast (Mediterranean Sea): patterns of spatial distribution

This study reports on the distribution of polychaete assemblages along a depth gradient from 5 to 25 m, along a stretch of rocky coast near Otranto (South Adriatic sea, Italy). Three depths were sampled in May and November 2000. At each depth three sites (about 100 m apart) were sampled by scraping off three replicate quadrats of 20×20 cm. The experimental design enabled identification of across- and along-shore spatial patterns of variation of polychaete assemblages. A total of 4,168 specimens, belonging to 152 taxa were collected. Multivariate analysis showed that the polychaete assemblages differed significantly among depths with the clearest differences between the shallowest sites (5 m) and the deeper ones (15–25 m). A considerable source of variation among sites at each level of the shore was also exhibited by the analyses, with the greatest differences among sites within depths recorded at 5 m. The species most contributing to the differentiation of assemblages among depths and sites within each depth were identified. Some potential causes of the observed differences are hypothesized and discussed. The importance of quantitative observation to provide the context for studying the underlying ecological processes is also stressed.Communicated by R. Cattaneo-Vietti, Genova     

Variation in benthic communities of eastern Caribbean coral reefs in relation to surface sediment composition

The effects of sedimentation on coral reefs are commonly studied at local scales, but larger-scale patterns have been elusive, making it difficult to determine the role of sedimentation in region-wide changes in these ecosystems. We examined the relationships between characteristics of reef-associated surface sediment and benthic composition of 22 reefs around 11 islands of the eastern Caribbean. The terrigenous fraction in surface sediment increased with proximity to a clear source of sediment input. The percent cover of live coral, macroalgae, and turf algae decreased with higher terrigenous sediment fraction, while sponge cover increased. Sites with sediment containing high and low terrigenous fraction differed in coral species assemblages. In particular, the cover of Montastraea annularis complex decreased with increasing terrigenous sediment fraction. The proportion of fine-grained sediment had no effect on benthic composition. These results suggest that sedimentation may play a role in shaping coral reef communities at a regional scale.     

Biotic indexes reveal the impact of harbour enlargement on benthic fauna

Environmental effects of enlargement works in Puerto Calero (Lanzarote, Canary Islands) were analysed in the sediments using abiotic variables (total hydrocarbons, polyaromatic hydrocarbons, organic matter and granulometry) and three biotic indexes (AMBI, M-AMBI and BENTIX). A before–after/control–impact (BACI) design was developed with four sampling campaigns, before (November 2004), during (March and July 2005) and after (July 2006) works. Inner stations were characterised by high concentrations of pollutants (total hydrocarbons and polyaromatic hydrocarbons). A temporal trend (2004–2006) was observed in macrofaunal assemblage structure, and thus in AMBI, M-AMBI and BENTIX indexes. Macrobenthic assemblages also mirrored the pollution gradient, with bioindicator species in inner stations (the polychaete Pseudopolydora paucibranchiata and the mollusc Abra alba), sensitive species (the sipunculid Aspidosiphon muelleri, the crustacean Pariambus typicus and the polychaete Aponuphis bilineata) in outer stations and ubiquitous species (the polychaetes Aricidea assimilis and Armandia polyophthalma) in both stations (inner and outer).     

Responses of fish assemblage structures to sandy beach types in Kyushu Island, southern Japan

To determine differences in fish assemblage structures between beach morphodynamic types on an exposed sandy shore, three beach types (reflective, intermediate, and dissipative) were sampled at Fukiagehama Beach, Kyushu Island, southern Japan, in May, August, and November 2006 and 2007. Distinct differences in physical conditions and the amount of major prey invertebrates, such as copepods, mysids, and amphipods, were recognized between the three beach types. The reflective beach was characterized mainly by turbulent swashes, coarse sediment, and a low abundance of major prey invertebrates. In contrast, the dissipative beach was characterized mostly by benign swashes, fine sediment, and a high abundance of prey invertebrates. The intermediate beach tended toward an intermediate condition between the reflective and dissipative beaches. The fish assemblage structures also differed clearly between the three beach types, with species and individual numbers being greatest on the dissipative beach and lowest on the reflective beach. A similarity index indicated differences in species composition of the assemblages between the beach types. Such differences arose primarily from the differential distributions of two dominant trophic groups, zooplankton (mostly copepods) and epibenthic crustacean (mainly mysids and amphipods) feeders, between the beach types, both groups tending to increase in species and individual numbers from the reflective beach to the dissipative beach. In addition, the mean standard length of all fish collected in each month tended to decrease toward the dissipative beach. These results suggested that beach types strongly influence sandy beach fish assemblage structures.     

Are soil mite assemblages structured by the identity of native and invasive alien grasses?

Associations between plants and animals in aboveground communities are often predictable and specific. This has been exploited for the purposes of estimating the diversity of animal species based on the diversity of plant species. The introduction of invasive alien plants into an ecosystem can result in dramatic changes in both the native plant and animal assemblages. Few data exist at the species level to determine whether belowground animal assemblages share the same degree of association to plants. The hypotheses that soil mites (Acari) form assemblages specifically associated with different native grass species in an unmanipulated natural ecosystem and that invasive alien grasses will impact soil mite assemblage composition in this setting were tested. Soil mites sampled beneath five native and two invasive alien species of grasses at the Konza Prairie Biological Station, Kansas, USA, were similarly abundant, species rich, diverse, and taxonomically distinct. No mite species had affinities for a specific grass species. There was no evidence from analysis of similarity, canonical correspondence analysis, or a nonparametric assemblage analysis that the assemblage composition of soil mites was specific to grass species. Results suggest that soil mite assemblages were more related to characteristics of the plant assemblage as a whole or prevailing soil conditions. The most recent invasive alien grass did not support a successionally younger mite fauna, based on the ratio of mesostigmatid to oribatid mites, and neither of the two invasive grasses influenced mite assemblage structure, possibly because they had not yet substantially altered the soil environment. Our results suggest that extrapolations of soil mite diversity based on assumptions of plant specificity would be invalid.     

Effects of crowding due to habitat loss on species assemblage patterns

Terrestrial animals are negatively affected by habitat loss, which is assessed on a landscape scale, whereas secondary effects of habitat loss, such as crowding, are usually disregarded. Such impacts are inherently hard to address and poorly understood, and there is a growing concern that they could have dire consequences. We sampled birds throughout a deforestation process to assess crowding stress in an adjacent habitat remnant in the southern Brazilian Atlantic Forest. Crowding is expected of highly mobile taxa, especially given the microhabitat heterogeneity of Neotropical forests, and we hypothesized that the arrival of new individuals or species in refuges shifts assemblage patterns. We used point counts to obtain bird abundances in a before-after-control-impact design sampling of a deforestation event. Temporal changes in taxonomic and functional diversity were examined with metrics used to assess alpha and beta diversity, turnover of taxonomic and functional similarity, and taxonomic and functional composition. Over time increased abundance of some species altered the Simpson index and affected the abundance-distribution of traits in the habitat remnant. Taxonomic composition and functional composition changed in the remnant, and thus bird assemblages changed over time. Taxonomic and functional metrics indicated that fugitives affected resident assemblages in refuges, and effects endured >2 years after the deforestation processes had ceased. Dissimilarity of taxonomic composition between pre- and postdeforestation assemblages increased, whereas functional composition reverted to preimpact conditions. We found that ecological disruptions resulted from crowding and escalated into disruptions of species’ assemblages and potentially compromising ecosystem functioning. It is important to consider crowding effects of highly mobile taxa during impact assessments, especially in large-scale infrastructure projects that may affect larger areas than is assumed.     

The infaunal benthos of a natural oil seep in the Santa Barbara channel

We are studying a diverse infaunal benthic community that exists in the fine sand sediments of a shallow (16 m) natural oil seep near Santa Barbara, California, USA. The study area and sampling methods are described in this introductory paper. Data presented indicate the adequacy of sampling in revealing horizontal patchiness and vertical faunal distributions. The infauna of the seep and of a nearby comparison area, without seepage but of similar depth and sediment type, are compared. The data indicate a consistently larger but fluctuating density of organisms at the seep station. However, Shannon-Weaver diversity (H=1.6 to 1.7), Peilou's evenness (J=0.80 to 0.81), and measures of dominance-diversity with estimates of graphical skewness (0.66 to 0.68) and kurtosis (1.2 to 1.4) are all similar for the two stations. The rank correlation of common species at the stations is significant according to Spearman's rho. Species common to both stations account for 85 to 95% of the individuals, further indicating the high degree of similarity between stations. Denser populations of oligochaetes and the maldanid polychaete Praxillella affinis pacifica suggest some advantages for deposit feeders at the seep station. Mats of the bacterium Beggiatoa sp. are associated with localized intense oil seepage. Hypotheses suggesting trophic enrichment and biochemical adaptation at the seep are presented.     

Microbial reaction rates and bacterial communities in sediment surrounding burrows of two nereidid polychaetes (Nereis diversicolor and N. virens)

The effects of infaunal mode of life on sediment properties, microbial reaction rates, as well as abundance and composition of bacterial communities were studied in sediment surrounding burrows (mucus lining, oxidised wall, ambient anoxic and surface sediment) of two closely related, but behaviourally different, nereidid polychaete worms: the facultative suspension-feeder Nereis (Hediste) diversicolor and the obligate deposit-feeder Nereis (Neanthes) virens. Burrow sediment of the two species was collected from two adjacent (50 m distance) shallow sandy locations (Kertinge Nor, Denmark). The burrow lining and wall of both polychaete species were enriched in organic matter originating from mucous secretions by the inhabitants and phytoplankton trapped through irrigation. This was more evident for N. diversicolor that shows a significantly higher irrigation rate than N. virens. Both the organic matter mineralisation rates (based on anaerobic incubations) and bacterial abundance were higher along the burrow linings and walls. However, accumulation of porewater TCO₂ and dissolved organic carbon in sediments adjacent to burrows increased most rapidly in the presence of N. diversicolor, suggesting higher heterotrophic activity associated with this species. Surprisingly, bacterial abundance was lower around burrows of N. diversicolor than those from N. virens indicating that burrow environments from the first species harbour a more active bacterial community. Molecular fingerprints of the 16S rRNA gene from bacterial communities showed that the composition of the burrow linings and walls resembled the ambient anoxic sediment rather than the oxic sediment surface. On the other hand, the bacterial fingerprints of the sediment surrounding the burrows of the two polychaete species were markedly different suggesting either a site-specific difference in sediment parameters or a significant species-specific impact of the burrow inhabitants.     

Benthic foraminifera assemblages at Great Meteor Seamount

Foraminiferal assemblages found at Great Meteor Seamount were studied in August 1998. Communities of living foraminifera in surface sediments from the plateau (290–325 m water depth) and from the surrounding base (2,300–4,096 m) were compared in abundances, diversity, and species composition. In this oligotrophic region, densities were very low, but diversity was high. Highest numbers were observed at the deep stations north, south, and east of the seamount and at the shallow station in the north of the plateau. Lowest densities were recorded southwest of the plateau centre and at the lee side of the seamount. We explain this distribution pattern with variable amounts of fresh organic material, caused by local oceanic currents. Generally, plateau stations indicated coarser sediments, lower organic carbon content, and higher temperatures. The foraminiferal fauna showed bathyal to abyssal characteristics and similarities to assemblages previously described from other parts of the North Atlantic and other oceans. Several dominant species extended between the two habitats, on the plateau and in the surrounding deep sediments, but other species were found exclusively at deep stations, at plateau stations, or at the abyssal reference station.Communicated by O. Kinne, Oldendorf/Luhe     

Sedimentary Pigments and Organic Matter in Relation to Benthic Fauna in the Tan-Shui Estuary, Taiwan

The benthic ecological structure of the Tan-Shui estuary, Taiwan is changed due to long term effects of dumping of urban wastewater and of engineering actions. to monitor these changes, we sampled and analyzed benthos and sediment from 12 stations on the estuary.

The composition of the dominant species of benthos varied seasonally, with molluscan and crustacean species having greater numbers and higher frequencies of occurrence than other species. the dominant taxa during winter were Nassarius sp. and Maldanidae at two stations. Analysis using Simpson's index and Shannon's index showed the benthic community varied more in coastal areas than in offshore areas.

Physicochemical analysis showed that most of the Tan-Shui estuary consisted of sandy sediment. the variations in concentrations of organic carbon and total nitrogen at each station were small. Although the concentrations of chlorophyll-a and carotenoid at all stations were generally low, the two stations had the highest concentrations, and we concluded that the concentration of pigments in these sediments was related to the abundance of benthos. the community structure of the benthos reflected the characteristics of the sediments, and benthic species exhibited selection of and adaptation to specific sedimentary environments.     

Sedimentary Pigments and Organic Matter in Relation to Benthic Fauna in the Tan-Shui Estuary,Taiwan

The benthic ecological structure of the Tan-Shui estuary, Taiwan is changed due to long term effects of dumping of urban wastewater and of engineering actions. to monitor these changes, we sampled and analyzed benthos and sediment from 12 stations on the estuary.

The composition of the dominant species of benthos varied seasonally, with molluscan and crustacean species having greater numbers and higher frequencies of occurrence than other species. the dominant taxa during winter were Nassarius sp. and Maldanidae at two stations. Analysis using Simpson's index and Shannon's index showed the benthic community varied more in coastal areas than in offshore areas.

Physicochemical analysis showed that most of the Tan-Shui estuary consisted of sandy sediment. the variations in concentrations of organic carbon and total nitrogen at each station were small. Although the concentrations of chlorophyll-a and carotenoid at all stations were generally low, the two stations had the highest concentrations, and we concluded that the concentration of pigments in these sediments was related to the abundance of benthos. the community structure of the benthos reflected the characteristics of the sediments, and benthic species exhibited selection of and adaptation to specific sedimentary environments.